One-step method for preparing a lithiated silicon electrode

ABSTRACT

In a one-step method for preparing a lithiated silicon electrode, a suspension of a lithium precursor and a silicon precursor in a carrier liquid is plasma sprayed without a carrier gas. The carrier liquid is water, alcohol, ethylene glycol, or mixtures thereof. The lithium precursor is selected from the group consisting of a lithium phosphate, a lithium nitrate, a lithium sulfate, a lithium carbonate, and combinations thereof. The suspension excludes an active carbon material and a binder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/912,462, filed Dec. 5, 2013, which isincorporated by reference herein in its entirety.

BACKGROUND

Secondary, or rechargeable, lithium-sulfur batteries or lithium ionbatteries are often used in many stationary and portable devices, suchas those encountered in the consumer electronic, automobile, andaerospace industries. The lithium class of batteries has gainedpopularity for various reasons including a relatively high energydensity, a general nonappearance of any memory effect when compared toother kinds of rechargeable batteries, a relatively low internalresistance, and a low self-discharge rate when not in use. The abilityof lithium batteries to undergo repeated power cycling over their usefullifetimes makes them an attractive and dependable power source.

SUMMARY

In an example of a one-step method for preparing a lithiated siliconelectrode, a suspension of a lithium precursor and a silicon precursorin a carrier liquid is plasma sprayed without a carrier gas. The carrierliquid is water, alcohol, ethylene glycol, or mixtures thereof. Thelithium precursor is selected from the group consisting of a lithiumphosphate, a lithium nitrate, a lithium sulfate, a lithium carbonate,and combinations thereof. The suspension excludes an active carbonmaterial and a binder. A pre-lithiated silicon electrode is alsodisclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the present disclosure willbecome apparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

FIG. 1 is a schematic, perspective view of an example of a system forperforming an example of a one-step method for preparing a lithiatedsilicon electrode; and

FIG. 2 is a schematic, perspective view of an example of alithium-sulfur battery showing a charging and discharging state, thebattery including an example of a pre-lithiated silicon anode accordingto the present disclosure.

DETAILED DESCRIPTION

The high theoretical capacity (e.g., 4200 mAh/g) of silicon renders itdesirable for use as a negative electrode (e.g., anode) material inlithium-sulfur batteries. However, it has been found that negativeelectrode materials with high specific capacities also have large volumeexpansion and contraction during charging/discharging of the lithium ionbattery. The large volume change (e.g., about 400%) experienced by thenegative electrode material during charging/discharging causes siliconparticles to fracture, decrepitate, or otherwise mechanically degrade,which results in a loss of electrical contact and poor life cycling.Poor cycling performance often includes a large capacity fade, which mayresult from the breakdown of contact between the negative electrodeactive material and conductive fillers in the negative electrode due tothe large volume change. Many silicon electrodes include arrays ofsilicon wires or rods, or porous silicon films in order to accommodatethe volume expansion during charging/discharging.

The volume expansion of silicon limits the manufacturing processes thatmay be used to form silicon-based electrodes having good performance.For example, a calendering process (which is used in many traditionalelectrode manufacturing processes) is generally not suitable because thesilicon electrode tends to crack during this process. In addition, thevolume expansion of silicon limits the characteristics of the electrode,such as silicon loading and thickness, when traditional processes areutilized. For example, a silicon loading over 4 mg/cm² and a thicknessover 250 μm may result in cracking of the silicon electrode when exposedto conditions (e.g., residual stress during drying) associated withtraditional electrode forming processes.

In addition to the limitations noted above, traditional siliconelectrode processing techniques also require an additional lithiationstep. This additional lithiation step is eliminated in the methoddisclosed herein.

The one-step method disclosed herein involves plasma spraying asuspension of nano- or micro-sized (i.e., diameter or average diameterranging from about 0.1 nm to about 200 μm) lithium and silicon precursorparticles. In some examples, the particle size of the suspensioncomponents ranges from about 1 nm to about 10,000 nm. In anotherexample, the nanoparticle size may range from about 40 nm to about 70nm. The solvent used in the suspension provides a cooling effect, sothat unlike traditional powder spray processes, particles withtrajectories along the edge or outside the plasma jet or flamesubstantially retain their spherical or unmelted shape. During thisprocess, particles with trajectories along the hot zones of the plasmajet or flame form splats (i.e., small particles that aggregate togetherand form concentrated flat shapes) on the surface. This combination ofspherical particles and splats results in a relatively dense lithiatedsilicon electrode that also exhibits a porosity ranging from about 15%to about 60% (without the use of a calendering process), which issuitable to accommodate volume expansion during discharge/charge cycles.In another example, the lithiated silicon electrode exhibits a porosityranging from about 30% to about 50%. As such, using the method(s)disclosed herein, it is believed that nano-sized particles of siliconmay be used to achieve a lithiated silicon electrode that has at least 4mg/cm² silicon loading which achieves a desirable cell level energydensity (e.g., >300 Wh/kg). This is unlike other methods in which thesurface:volume ratio renders it difficult to achieve a desirable siliconloading with nano-sized particles.

As mentioned above, the method disclosed herein utilizes plasma sprayingof a suspension to form a lithiated silicon electrode without additionalprocessing steps, such as lithiation and calendering. FIG. 1schematically illustrates an example of a system 10 for forming thelithiated silicon electrode 12.

The suspension 14 used in the examples disclosed herein includes asilicon precursor 16, a lithium precursor 18, and a carrier liquid 20.In some examples, the suspension 14 includes no other components. Inother examples, the suspension 14 includes metal-organic precursorsdispersed in isopropanol, or polymeric complexes. In still otherexamples, the suspension 14 includes a dispersant that aids indispersing the silicon precursor 16 and the lithium precursor 18throughout the selected carrier liquid 20. In each example of thesuspension 14, it is to be understood that the suspension 14 does notinclude an active carbon material or a binder. As such, the resultingelectrode 12 that is formed is also free of active carbon material andbinder.

The final suspension 14 has a solid content up to 30% in some examplesand up to 40% in other examples, a dispersant amount up to 5%, and abalance of the carrier liquid 20.

The silicon precursor 16 is a silicon nanopowder. The nanopowderparticles have an average diameter ranging from about 1 nm to about 100nm. The amount of silicon precursor 16 used in the suspension 14 isenough to form the electrode 12 having a silicon loading of at least 4mg/cm². In an example, the silicon loading in the final electrode 12ranges from greater than 4 mg/cm² to about 8 mg/cm². Examples of thesilicon precursors 16 include 2,4,6,8,10-pentamethylcyclopentasiloxane(CH₃SiHO)₅, pentamethyldisilane (CH₃)₃SiSi(CH₃)₂H, silicon tetrabromide(SiBr₄), silicon tetrachloride (SiCl₄), tetraethylsilane Si(C₂H₅)₄, and2,4,6,8-tetramethylcyclotetrasiloxane (HSiCH₃O)₄.

In an example, the lithium precursor 18 is a lithium nanopowder. Similarto the silicon nanopowder, the lithium particles also have an averagediameter ranging from about 1 nm to about 100 nm. The lithium precursor18 may be a lithium phosphate, a lithium nitrate, a lithium sulfate, alithium carbonate, or combinations thereof. The lithium precursor 18 mayalso be in the form of polymer coated lithium nano-particles. Stillfurther, lithium amides, such as Li bis(ethyldimethylsilyl)amides, maybe used. These amides are prepared by deprotonation of parent aminesusing butyl lithium. In still other examples, a class of liquid lithiumprecursors may be used, which includes amides with SiM₂R² and (SiM₂R²)₂,where M is Li, R²=ethyl, n-propyl, i-propyl, n-butyl, n-hexyl, n-octylin t-buyl or t-anyl.

In an example, the final suspension 14 is a 100 mL solution with thesilicon precursor 16 (e.g., 2,4,6,8,10-pentamethylcyclopentasiloxane(CH₃SiHO)₅) and the lithium precursor 18 (e.g., lithium phosphate)present in a ratio of 50:50.

The liquid carrier 20 may be water, an alcohol (e.g., ethanol,n-propanol, i-propanol, n-butanol), ethylene glycol, or any mixtures ofthese components may be used (e.g., a mixture of water and alcohol, amixture of water and ethylene glycol, etc.).

As noted above, in some examples the suspension 14 also includes ametal-organic precursor dispersed in isopropanol. Examples of themetal-organic precursor include aluminum heptanedionate as a precursorfor alumina, triethylsilane as a precursor for silica, or titaniumtetrakisdiethylamide as a precursor for titania. The metal-organicprecursor may be present in an amount ranging from 1 wt % to about 50 wt% of the total wt % of the suspension 14.

In other examples of the suspension 14, a polymeric complex is added tothe silicon precursor 16, the lithium precursor 18, and the carrierliquid 20. Organic acids may be used as the polymeric complex, examplesof which include citrate, acetate, tartarate, formates, oxalate, and/orlactate. The polymeric complex may be selected to enhance the flow ofthe suspension 14 and/or to enhance the thermal properties of theelectrode 12 that is formed. The polymeric complex may be present in anamount ranging from 1 wt % to about 10 wt% of the total wt % of thesuspension 14.

Depending on the precursors 16, 18 (e.g., type, size, etc.) and thecarrier liquid 20 that are selected, the suspension 14 may also includea dispersant to aid dispersing the precursors 16, 18 and to keep themfrom settling in the carrier liquid 20. The dispersant may be includedin an amount ranging from about 0.1 wt % to about 5 wt % of the total wt% of the suspension 14. Examples of suitable dispersants includeoligomeric dispersants and ethyl alcohol.

The system 10 shown in FIG. 1 also includes a plasma spray system 22.The plasma spray system 22 includes a plasma source 24 and a suspensionfeeding system 26, 26′, 26″.

The plasma source 24 includes a plasma torch, which generates a plasmajet 28. The plasma torch may create the plasma jet 28 using gas (e.g.,air) and direct current (DC), alternating current (AC), or radiofrequency (RF), and the plasma jet 28 may be gas-stabilized and/orwater-stabilized. The spraying environment may involve air plasmaspraying (APS), high velocity oxygen fuel spraying (HVOF), or vacuumspraying plasma (VPS).

The plasma source 24 is operated at relatively high current (e.g., 600to 800 Amps) and low voltage (e.g., 60 to 80 Volts). The plasma sprayingis also a high energy process (i.e., particle velocity higher than 2Mach). In an example the temperature of the plasma spraying is less than150° C. In another example, the temperature of plasma spraying rangesfrom about 37° C. to about 93° C. Still further, in another example thetemperature of the plasma spraying ranges from about 60° C. to about 70°C. It is believed that the combination of high energy and temperatureleads to minimal incorporation of contaminants into the electrode 12.Furthermore, these temperatures are low enough to avoid degradation ofthe substrate 30.

It is to be understood that the spray parameters (e.g., current, plasmapower, particle flight, temperature, feed rate, etc.) and suspension 14parameters (e.g., particle size, constituent phases, grain size,flowability, etc.) may be adjusted in order to avoid any overheatingand/or to control features (e.g., thickness, morphology, porosity,density, etc.) of the electrode 12.

The suspension feeding system 26, 26′, 26″ may be integrated into theplasma source 24 or may be a stand-alone unit. Different examples of thesuspension feeding system 26, 26′, 26″ are shown in FIG. 1. In anexample (labeled “1” in FIG. 1), the suspension feeding system 26delivers the suspension 14 as a fine liquid-based stream directly intothe plasma jet 28. In another example (labeled “2” in FIG. 1), thesuspension feeding system 26′ injects the suspension 14 directly into acombustion chamber of the plasma torch. In still another example(labeled “3” in FIG. 1), the suspension feeding system 26″ injects thesuspension 14 into an atomizer 32, which atomizes or nebulizes thesuspension 14 into droplets that are introduced into the plasma jet 28.It is to be understood that the plasma spray system 22 does not utilizea carrier gas to introduce the precursors 16, 18, but rather uses thecarrier liquid 20 of the suspension 14, to deliver the precursors 16, 18to the plasma jet 28.

In the plasma jet 28, the suspension 14, in the form of the liquid-basedstream or the droplets, is fragmented due, at least in part, to the flowand shear forces. The carrier liquid 20 in the suspension 14 isvaporized and evaporated. The evaporation of the carrier liquid 20provides a cooling effect for the plasma jet 28 at its edges andextending outward into the environment surrounding the plasma jet 28.The cooled areas allow at least some of the precursor particles 16, 18(those having their trajectory along these areas) within the plasma jet28 to retain their spherical or unmelted shapes upon being deposited. Inspite of the cooling effect, it is believed that the plasma jet 28 stillincludes hot zones, and particles 16, 18 having a trajectory along thesezones of the plasma jet 28 will melt or soften and form splats (i.e.,aggregates that are flatter compared to the spherical shape) upon beingdeposited. In one example, the particles 16, 18 deposited to form thesplats are at least partially melted. In another example, the particles16, 18 deposited to form the splats are fully melted. In still anotherexample, the particles 16, 18 deposited to form the splats are a mixtureof partially melted and fully melted particles 16, 18. The melting stateof the particles 16, 18 may be controlled by controlling a temperatureof the plasma spraying and by controlling a feed rate of the suspension14.

The cooling effect from the carrier liquid 20 provides enough coolingthat additional cooling processes or mechanisms are not utilized in themethod disclosed herein.

The plasma jet 28 accelerates the precursor particles 16, 18 toward asubstrate 30, which may be a current collector (that remains in contactwith the final electrode 12) or any other base material. In someexamples, a removable support may be used that can be peeled away fromthe electrode 12 so that a free-standing electrode 12 is formed. Theremovable support may also remain in contact with the electrode 12 ifthat is desirable.

The previously mentioned cooling effect is also believed to enhance thebond strength, and thus the adhesion, between the electrode 12 that isformed and the underlying substrate 30. In an example, pull strengthsranging from 8,000 psi to 10,000 psi (per ASTM C633 tests) may beachieved.

The plasma spraying of the suspension 14 may be continued for a suitabletime to generate the electrode 12 having a desirable thickness. Theamount of time that the plasma spraying of the suspension 14 is carriedout for may vary depending on the line speed and feed rate. Generally, ahigher line speed results in a faster plasma spraying of the suspension14. For example, the line speed may be 1000 mm/s and the feed rate mayrange from about 200 mL/s to about 500 mL/s. In an example, thethickness ranges from about 0.1 μm to about 100 μm, or more (e.g., up toabout 200 μm). In another example, the thickness ranges from 1 μm toabout 20 μm. The thickness that may be achieved per pass of the plasmaspray depends, at least in part, on the process/spray parameters. Assuch, multiple spraying passes may be required in order to achieve adesired thickness.

The distance 34 between the end of the plasma source 24 and thesubstrate 30 may range from about 1 cm to about 50 cm. In some examples,a desired range is from about 5 cm to about 10 cm. This relatively shortdistance may be utilized because of the cooling effect introduced by thecarrier liquid 20 and because the inertia of the particles 16, 18 is low(due in part to relatively stable plasma conditions, such as temperatureand velocity).

The method disclosed herein provides a stable, pulse-free suspensionstream in order to produce a reproducible, high quality electrode 12.The electrode 12 morphology and properties may be affected by the natureof the suspension 14, the mode by which the suspension 14 is injected,and the spraying parameters. By varying one or more of these factors,the density and/or porosity of the electrode 12 may be controlled. As anexample, if larger particles are used in the suspension 14, a densercoating with large pores would be formed. A suitably dense coating maybe obtained by selecting a particle size that is not too large but nottoo small (i.e., medium sized particles in accordance with the particlesize range provided herein). In any of the examples disclosed herein,the resulting electrode 12 is believed to be free of defects (e.g.,cracks, etc.)

The lithiated silicon electrode 12 that is formed may be used as thenegative electrode or anode of a lithium-sulfur battery. An example ofthe lithium-sulfur battery 40 including the electrode 12 as the anode isschematically shown in FIG. 2. The battery 40 generally includes theanode 12, a cathode 36, and a porous polymer separator 42. Thelithium-sulfur battery 40 also includes an interruptible externalcircuit 44 that connects the anode 12 and the cathode 36. Each of theanode 12, the cathode 36, and the porous polymer separator 42 are soakedin an electrolyte solution that is capable of conducting lithium ions.

The porous polymer separator 42, which operates as both an electricalinsulator and a mechanical support, is sandwiched between the anode 12and the cathode 36 to prevent physical contact between the twoelectrodes 12, 36 and the occurrence of a short circuit. While notshown, it is to be understood that barrier layer(s) may be formedbetween the porous polymer separator 42 and the cathode 36 in order toprevent the passage of polysulfide ions across the porous polymerseparator 42. The porous polymer separator 42, in addition to providinga physical barrier between the two electrodes 12, 36, ensures passage oflithium ions (identified by the Li⁺) and some related anions through theelectrolyte solution filling its pores.

The porous polymer separator 42 may be formed of a polyolefin membrane.The polyolefin may be a homopolymer (derived from a single monomerconstituent) or a heteropolymer (derived from more than one monomerconstituent), and may be either linear or branched. If a heteropolymerderived from two monomer constituents is employed, the polyolefin mayassume any copolymer chain arrangement including those of a blockcopolymer or a random copolymer. The same holds true if the polyolefinis a heteropolymer derived from more than two monomer constituents. Asexamples, the polyolefin may be polyethylene (PE), polypropylene (PP), ablend of PE and PP, or multi-layered structured porous films of PEand/or PP. Commercially available porous polymer membranes includesingle layer polypropylene membranes, such as CELGARD 2400 and CELGARD2500 from Celgard, LLC (Charlotte, N.C.). It is to be understood thatthe membrane may be uncoated or untreated. For example, the membrane maynot include any surfactant treatment thereon. In other examples, themembrane may be treated with a surfactant.

The porous polymer separator 42 may also be formed from another polymerchosen from polyethylene terephthalate (PET), polyvinylidene fluoride(PVdF), polyamides (Nylons), polyurethanes, polycarbonates, polyesters,polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI),polyamide-imides, polyethers, polyoxymethylene (e.g., acetal),polybutylene terephthalate, polyethylenenaphthenate, polybutene,polyolefin copolymers, acrylonitrile-butadiene styrene copolymers (ABS),polystyrene copolymers, polymethylmethacrylate (PMMA), polyvinylchloride (PVC), polysiloxane polymers (such as polydimethylsiloxane(PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), polyphenylenes(e.g., PARMAX™ (Mississippi Polymer Technologies, Inc., Bay Saint Louis,Miss.)), polyarylene ether ketones, polyperfluorocyclobutanes,polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers andterpolymers, polyvinylidene chloride, polyvinylfluoride, liquidcrystalline polymers (e.g., VECTRAN™ (Hoechst AG, Germany) and ZENITE®(DuPont, Wilmington, Del.)), polyaramides, polyphenylene oxide, and/orcombinations thereof. It is believed that another example of a liquidcrystalline polymer that may be used for the separator 42 ispoly(p-hydroxybenzoic acid). In yet another example, the porous polymerseparator 42 may be chosen from a combination of the polyolefin (such asPE and/or PP) and one or more of the polymers for the membrane 16 listedabove.

The porous polymer separator 42 may be a single layer or may be amulti-layer (e.g., bilayer, trilayer, etc.) laminate fabricated fromeither a dry or wet process. For example, a single layer of thepolyolefin and/or other listed polymer may constitute the entirety ofthe porous polymer separator 42. As another example, however, multiplediscrete layers of similar or dissimilar polyolefins and/or polymers maybe assembled into the porous polymer separator 42. In one example, adiscrete layer of one or more of the polymers may be coated on adiscrete layer of the polyolefin to form the porous polymer separator42. In some instances, the separator 42 may include fibrous layer(s) toimpart appropriate structural and porosity characteristics.

As mentioned above, the anode 12 is the lithiated silicon electrodeformed by the suspension plasma spraying process disclosed herein. Inthe example shown in FIG. 2, the anode 12 is formed on the substrate 30,which is a negative-side current collector. The negative-side currentcollector 30 may be formed from copper or any other appropriateelectrically conductive material known to skilled artisans. Thenegative-side current collector 30 collects and moves free electrons toand from the external circuit 44.

The cathode 36 of the lithium-sulfur battery 40 may be formed from anysulfur-based active material that can sufficiently undergo alloying anddealloying with aluminum or another suitable current collector 38functioning as the positive terminal of the lithium-sulfur battery 40.Examples of sulfur-based active materials include S₈, Li₂S₈, Li₂S₆,Li₂S₄, Li₂S₂, and Li₂S. Another example of the sulfur-based activematerial may be a sulfur-carbon composite. The cathode 36 may beencapsulated with carbon and may also include a polymer binder materialto structurally hold the sulfur-based active material together. Thepolymeric binder may be made of at least one of polyvinylidene fluoride(PVdF), polyethylene oxide (PEO), an ethylene propylene diene monomer(EPDM) rubber, carboxymethyl cellulose (CMC), styrene-butadiene rubber(SBR), styrene-butadiene rubber carboxymethyl cellulose (SBR-CMC),polyacrylic acid (PAA), cross-linked polyacrylic acid-polyethylenimine,polyvinyl alcohol (PVA), polyimide, poly(acrylamide-co-diallyl dimethylammonium chloride), sodium alginate, or other water-soluble or organicsolvent-based binders.

A positive-side current collector 38 may be formed from aluminum or anyother appropriate electrically conductive material known to skilledartisans. The positive-side current collector 38 collects and moves freeelectrons to and from the external circuit 44.

Any appropriate electrolyte solution (not shown) that can conductlithium ions between the anode 12 and the cathode 36 may be used in thelithium-sulfur battery 40. In one example, the non-aqueous electrolytesolution may be an ether based electrolyte that is stabilized withlithium nitrite. Other non-aqueous liquid electrolyte solutions mayinclude a lithium salt dissolved in an organic solvent or a mixture oforganic solvents. Examples of lithium salts that may be dissolved inether to form the non-aqueous liquid electrolyte solution includeLiClO₄, LiAlCl₄, LiI, LiBr, LiSCN, LiBF₄, LiB(C₆H₅)₄, LiAsF₆, LiCF₃SO₃,LiN(FSO₂)₂ (LiFSI), LiN(CF₃SO₂)₂ (LITFSI), LiPF₆, LiB(C₂O₄)₂ (LiBOB),LiBF₂(C₂O₄) (LiODFB), LiPF₄(C₂O₄) (LiFOP), LiNO₃, and mixtures thereof.The ether based solvents may be composed of cyclic ethers, such as1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and chainstructure ethers, such as 1,2-dimethoxyethane, 1-2-diethoxyethane,ethoxymethoxyethane, tetraethylene glycol dimethyl ether (TEGDME),polyethylene glycol dimethyl ether (PEGDME), and mixtures thereof.

The lithium-sulfur battery 40 may support a load device 46 that can beoperatively connected to the external circuit 44, which connects theanode 12 and cathode 36. The load device 46 receives a feed ofelectrical energy from the electric current passing through the externalcircuit 44 when the lithium-sulfur battery 40 is discharging. As such,the load device 46 may be powered fully or partially by the electriccurrent passing through the external circuit 44 when the lithium-sulfurbattery 40 is discharging. While the load device 46 may be any number ofknown electrically-powered devices, a few specific examples of apower-consuming load device include an electric motor for a hybridvehicle or an all-electrical vehicle, a laptop computer, a cellularphone, and a cordless power tool. The load device 46 may also, however,be a power-generating apparatus that charges the lithium-sulfur battery40 for purposes of storing energy. For instance, the tendency ofwindmills and solar panels to variably and/or intermittently generateelectricity often results in a need to store surplus energy for lateruse.

The lithium-sulfur battery 40 can include a wide range of othercomponents that, while not depicted here, are nonetheless known toskilled artisans. For instance, the lithium-sulfur battery 40 mayinclude a casing, gaskets, terminals, tabs, and any other desirablecomponents or materials that may be situated between or around the anode12 and the cathode 36 for performance-related or other practicalpurposes. Moreover, the size and shape of the lithium-sulfur battery 40,as well as the design and chemical make-up of its main components, mayvary depending on the particular application for which it is designed.Battery-powered automobiles and hand-held consumer electronic devices,for example, are two instances where the lithium-sulfur battery 40 wouldmost likely be designed to different size, capacity, and power-outputspecifications. The lithium-sulfur battery 40 may also be connected inseries and/or in parallel with other similar lithium-sulfur batteries 40to produce a greater voltage output and current (if arranged inparallel) or voltage (if arranged in series) if the load device 46 sorequires.

The lithium-sulfur battery 40 can generate a useful electric currentduring battery discharge (shown by reference numeral 50 in FIG. 2).During discharge, the chemical processes in the battery 40 includelithium (Li⁺) dissolution from the surface of the anode 12 andincorporation of the lithium cations into alkali metal polysulfide salts(i.e., Li₂S). As such, polysulfides are formed (sulfur is reduced) onthe surface of the cathode 36 in sequence while the battery 40 isdischarging. The chemical potential difference between the cathode 36and the anode 12 (ranging from approximately 1.5 to 3.0 volts, dependingon the exact chemical make-up of the electrodes 12, 36) drives electronsproduced by the dissolution of lithium at the anode 12 through theexternal circuit 44 towards the cathode 36. The resulting electriccurrent passing through the external circuit 44 can be harnessed anddirected through the load device 46 until the lithium in the anode 12 isdepleted and the capacity of the lithium-sulfur battery 40 isdiminished.

The lithium-sulfur battery 40 can be charged or re-powered at any timeby applying an external power source to the lithium-sulfur battery 40 toreverse the electrochemical reactions that occur during batterydischarge. During charging (shown at reference numeral 48 in FIG. 2),lithium plating to the anode 12 takes place and sulfur formation at thecathode 36 takes place. The connection of an external power source tothe lithium-sulfur battery 40 compels the otherwise non-spontaneousoxidation of lithium at the cathode 36 to produce electrons and lithiumions. The electrons, which flow back towards the anode 12 through theexternal circuit 44, and the lithium ions (Li⁺), which are carried bythe electrolyte across the porous polymer separator 42 back towards theanode 12, reunite at the anode 12 and replenish it with lithium forconsumption during the next battery discharge cycle. The external powersource that may be used to charge the lithium-sulfur battery 40 may varydepending on the size, construction, and particular end-use of thelithium-sulfur battery 40. Some suitable external power sources includea battery charger plugged into an AC wall outlet and a motor vehiclealternator.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range of about 1 nm to about 100 nm should be interpreted toinclude not only the explicitly recited limits of about 1 nm to about100 nm, but also to include individual values, such as 25 nm, 42 nm,90.5 nm, etc., and sub-ranges, such as from about 5 nm to about 75 nm;from about 20 nm to about 55 nm, etc. Furthermore, when “about” isutilized to describe a value, this is meant to encompass minorvariations (up to +/−5%) from the stated value.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it will beapparent to those skilled in the art that the disclosed examples may bemodified. Therefore, the foregoing description is to be considerednon-limiting.

What is claimed is:
 1. A one-step method for preparing a lithiatedsilicon electrode, the one step method comprising: plasma spraying,without a carrier gas, a suspension of a lithium precursor particle anda silicon precursor particle in a carrier liquid of water, alcohol,ethylene glycol, or mixtures thereof, the lithium precursor particlebeing selected from the group consisting of a lithium phosphate, alithium nitrate, a lithium sulfate, a lithium carbonate, andcombinations thereof, the silicon precursor particle and the suspensionexcluding an active carbon material and a binder.
 2. The one-step methodas defined in claim 1 wherein the suspension further includes a metalorganic precursor in isopropanol.
 3. The one-step method as defined inclaim 1 wherein the suspension further includes a polymeric complex. 4.The one-step method as defined in claim 1 wherein the suspension isintroduced as a liquid stream into plasma jet used in the plasmaspraying.
 5. The one-step method as defined in claim 1 wherein thesuspension is nebulized into droplets and then introduced into plasmajet used in the plasma spraying.
 6. The one-step method as defined inclaim 1 wherein the suspension further includes a dispersant.
 7. Theone-step method as defined in claim 1 wherein the suspension is plasmasprayed on a target substrate, and wherein a spray distance between aplasma torch and the target substrate ranges from about 1 cm to about 50cm.
 8. The one-step method as defined in claim 1 wherein the plasmaspraying is performed at a temperature less than or equal to 150° C. 9.The one-step method as defined in claim 1, further comprising adjustinga parameter of the plasma spraying to control a porosity of thelithiated silicon electrode.
 10. The one-step method as defined in claim1, further comprising controlling a temperature of the plasma sprayingto control a melting state of the lithium precursor and the siliconprecursor.
 11. The one-step method as defined in claim 10 wherein thelithium precursor and the silicon precursor form splats on a substrateupon which they are deposited, the splats being at least partiallymelted.
 12. The one-step method as defined in claim 1 wherein thecarrier liquid in the suspension causes a cooling effect during plasmaspraying, thereby increasing a bond strength between a substrate andsplats formed from the lithium precursor and the silicon precursordeposited on the substrate.
 13. The one-step method as defined in claim12 wherein the carrier liquid is water and no external cooling mechanismis used in the one-step method.
 14. The one-step method as defined inclaim 1, further comprising adjusting a parameter of the plasma sprayingto control a thickness of the lithiated silicon electrode such that thethickness ranges from about 0.1 μm to about 250 μm.
 15. A one-stepmethod for preparing a lithiated silicon electrode, the one step methodcomprising: plasma spraying, without a carrier gas, a suspension of alithium precursor nanopowder particle having an average diameter of lessthan or equal to about 100 nm and a silicon precursor nanopowderparticle having an average diameter of less than or equal to about 100nm in a carrier liquid of water, alcohol, ethylene glycol, or mixturesthereof, the lithium precursor being selected from the group consistingof a lithium phosphate, a lithium nitrate, a lithium sulfate, a lithiumcarbonate, and combinations thereof, the silicon precursor particle andthe suspension excluding an active carbon material and a binder.
 16. Theone-step method as defined in claim 15 wherein the plasma spraying isperformed at a temperature less than or equal to 150° C.
 17. Theone-step method as defined in claim 15 wherein the carrier liquid in thesuspension causes a cooling effect during plasma spraying, therebyincreasing a bond strength between a substrate and splats formed fromthe lithium precursor and the silicon precursor deposited on thesubstrate.
 18. The one-step method as defined in claim 17, wherein thebond strength has a pull strength ranging from 8,000 pound per squareinch (psi) to 10,000 psi.
 19. The one-step method as defined in claim 15wherein the carrier liquid is water and no external cooling mechanism isused in the one-step method.
 20. The one-step method as defined in claim15, further comprising adjusting a parameter of the plasma spraying tocontrol a thickness of the lithiated silicon electrode such that thethickness ranges from about 0.1 μm to about 250 μm.